bugfix:fix CME in ZK discovery implementation.

[xingfudeshi]

Ⅰ. Describe what this PR did

fix ConcurrentModificationException in Zookeeper discovery implementation.
Here, while traversing iZkChildListeners, new listener may be added, so CopyOnWriteArraylist must be used here to avoid CME.

Ⅱ. Does this pull request fix one issue?

fixex #1234

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #1239 into develop will decrease coverage by 0.02%.
The diff coverage is 100%.

@@              Coverage Diff              @@
##             develop    #1239      +/-   ##
=============================================
- Coverage      44.96%   44.93%   -0.03%     
  Complexity      1488     1488              
=============================================
  Files            253      253              
  Lines          10279    10279              
  Branches        1337     1337              
=============================================
- Hits            4622     4619       -3     
- Misses          5070     5072       +2     
- Partials         587      588       +1

Impacted Files	Coverage Δ	Complexity Δ
...very/registry/zk/ZookeeperRegisterServiceImpl.java	63.77% <100%> (ø)	24 <2> (ø)	⬇️
...server/store/file/FileTransactionStoreManager.java	46.34% <0%> (-1.05%)	19% <0%> (ø)

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[slievrly]

LGTM

[lovepoem]

lgtm